1. Field of the Invention
The present invention relates to a container and, more particularly, to a canopy in a container and a method of orienting the canopy in a fixed position.
2. Description of the Prior Art
Semiconductor technologies have developed rapidly in the past few decades, wherein optical lithography plays a critical role. Optical lithography is depended upon wherever a pattern needs to be defined.
When optical lithography is applied to semiconductors, a designed pattern is first made into a light-transmitting reticle having a particular shape. Then, a light source is projected through the reticle onto a silicon wafer to reveal a particular pattern by exposure. The reticle used for generating a pattern must be clean absolutely because any particles attached to the reticle (such as particles, powder dusts, or organic matters) will impair the quality of imaging through projection. Therefore, a clean room is always necessary for general wafer processes to prevent contamination by airborne particles. However, the clean rooms nowadays can not achieve an absolutely dust-free standard. Anti-contamination reticle pods are hence used in modern semiconductor processes for storing and transporting reticles in order to maintain the reticle cleaning process.
A conventional reticle pod is usually made of a macromolecular material. This kind of material provides such advantages as molding easily, low cost, and transparent. While this kind of material has a high electric resistance and is therefore nonconductive, it tends to generate static electricity from friction or general handling. Particularly in a clean room where humidity must be kept at a low level, electric charge can be very easily generated and accumulated on the reticle made of such material. Electrostatic charge on a surface of a reticle will attract particulate pollutants in the air or even result in an electrostatic discharge (ESD) from metal lines on the reticle. Once the static electricity discharge, a transient current is generated and may produce sparks or arcs. A strong current and a high temperature accompanying the sparks or arcs will eventually oxidize and melt the metal lines, thereby changing the pattern on the reticle.
Presently there are many solutions to the problems associated with electrostatic discharge. First of all is to improve the working environment, such as maintaining an appropriate humidity in the air, equipping operators with clothes having a grounding effect, or using ion fans to remove static electricity in the environment. However, the working environment may be changed by a plurality of unpredictable factors, so that it is impossible to completely prevent a reticle from being damaged by static electricity.
Another approach is to change the material of the reticle pod. For example, U.S. Pat. No. 6,513,654 disclosed a reticle support structure with a grounding function, in which the reticle support structure can release electrostatic charge on a reticle when a reticle pod is in contact with a matching table. As another example, U.S. Pat. No. 6,247,599 disclosed a conductive plate is disposed on the chassis or canopy of a reticle pod to reduce the accumulation of electric charge. While the method of adding an electrically conductive chassis has been widely adopted, the canopy and the chassis are positioned mainly by screws, which becomes a contamination source during a screwing process because the friction in the screwing process will generate particles and thus causes the contamination.
In view of the above, the present invention aims to improve the shortcomings of prior art reticle pods by providing a reticle pod disclosed herein.